Dicksonia berteroana (Juan Fernandez Tree Fern)
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Dicksonia berteroana
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Introduction & Discovery
Dicksonia berteroana is the tree fern of the Juan Fernandez Islands, the legendary archipelago in the south-eastern Pacific where the marooned Scottish sailor Alexander Selkirk provided the inspiration for Daniel Defoe's Robinson Crusoe, one of the foundational novels of English literature. These remote volcanic islands, rising from the floor of the Pacific some 670 kilometres off the Chilean coast, harbour one of the most extraordinary and endangered endemic floras on Earth, and Dicksonia berteroana is among its most striking botanical inhabitants, a tree fern whose presence on islands barely four million years old testifies to the notable power of fern spore dispersal across oceanic barriers. The species was named in honour of Carlo Giuseppe Bertero (1789 to 1831), an Italian physician and botanist from the town of Santa Vittoria d'Alba in Piedmont, who abandoned medicine for the passion of botanical collecting and spent years travelling through the Caribbean, Colombia, and Chile before visiting the Juan Fernandez Islands in the late 1820s. Bertero's collections from the archipelago were among the first systematic botanical documentation of the island's endemic flora and included numerous species new to science. Tragically, Bertero was lost at sea in April 1831 while returning from Tahiti aboard a vessel that was never heard from again, and the tree fern bearing his name serves as a living memorial to his dedication and sacrifice in the service of botanical knowledge. Dicksonia berteroana belongs to the family Dicksoniaceae, characterised by soft multicellular hairs at the stipe bases rather than the scales of the Cyatheaceae, and by marginal sori protected by bivalved indusia, characters confirmed by molecular phylogenetic analysis as diagnostic for a genuine evolutionary lineage. The species' presence on these young oceanic volcanic islands demonstrates that the Dicksonia lineage colonised by long-distance spore dispersal from continental or other island sources, crossing at least 670 kilometres of open ocean, an extraordinary feat that underscores the notable capacity of microscopic fern spores to bridge oceanic barriers that are impassable to most plant groups. Today the species is threatened by the same forces that imperil the entire Juan Fernandez endemic flora: invasive plant species, particularly the aggressive European blackberry (Rubus ulmifolius) and the native-turned-invasive maqui (Aristotelia chilensis), have colonised vast areas of former native forest, while feral goats and rabbits have degraded the forest understory and prevented natural regeneration. Conservation of D. berteroana is inseparable from the broader effort to protect and restore the Juan Fernandez flora, one of the highest priorities in South American and global plant conservation.
This extremely rare and beautiful tree fern is endemic only to Robinson Crusoe Island, one of the Juan Fernandez Islands off the coast of Chile, where it is found as an understorey plant in primary forest and is occasionally seen emergent on wet ridges. It sports a small trunk that can reach 4 to 5 m in height and supports a crown of spreading leaves to 2 m (7 ft.) long on blackish petioles. Peculiar, rust-colored hair covers the trunk and petioles. It is immediately clear that Dicksonia berteroana is much more similar and more closely related to the western Pacific species than to D. sellowiana of South America, with which it has little in common. It is very rare in cultivation but will thrive in any humid, cool temperate environment. Like most tree ferns it prefers humus-rich but well drained soils.
Discovery & Naming
The species commemorates Carlo Giuseppe Bertero (1789 to 1831), an Italian physician and passionate botanist from Santa Vittoria d'Alba in the Piedmont region of northern Italy. Bertero studied medicine and natural history at the University of Turin before beginning a life of botanical exploration in the Americas. He collected extensively in the Caribbean (Guadeloupe, Saint Thomas) and in Chile, where he arrived in 1827 and spent several years documenting the flora of central Chile and the Juan Fernandez Islands. His collections from the archipelago were among the first systematic botanical documentation of the island's extraordinary endemic flora and included type material for numerous species. In April 1831, Bertero departed Tahiti aboard the vessel that was lost at sea, and he was never heard from again. His collections, distributed to major European herbaria, continued to yield new species descriptions for decades after his death. The broader botanical exploration of the Juan Fernandez Islands continued through the nineteenth and twentieth centuries, with major contributions by Federico Johow (who published the first comprehensive account in 1896) and Carl Skottsberg (1880 to 1963), whose monumental Natural History of Juan Fernandez and Easter Island (1920 to 1956) provided the definitive treatment of the archipelago's flora and fauna. The genus Dicksonia was established by L'Heritier de Brutelle in 1789, honouring the English nurseryman James Dickson, and the family Dicksoniaceae is confirmed as distinct from Cyatheaceae in all modern classification systems.
Native Range & Distribution Map
Distribution map showing the native range of Dicksonia berteroana.
Biology & Frond Morphology
Dicksonia berteroana belongs to the genus Dicksonia in the family Dicksoniaceae, producing bipinnate to tripinnatifid fronds produced in a terminal crown from the single apical growing point of the trunk, reaching 1.5 to 2.5 metres in length on mature specimens. blades are broadly lanceolate, dark green above and paler beneath, with a moderately leathery texture suited to the humid but occasionally wind-exposed island conditions. pinnae are lanceolate, arranged alternately along the rachis, deeply pinnatifid to fully pinnate, with 15 to 25 pairs per frond. stipes are stout, 20 to 50 centimetres long, dark brown to blackish at the base, and clothed with soft rufous-brown multicellular hairs characteristic of the family dicksoniaceae, immediately distinguishing the species from any cyatheaceae, which bear scales or spines at the stipe bases. young croziers are enveloped in dense woolly tawny-brown indument that protects the developing tissues. sori are marginal, positioned at the tips of veins at the pinnule margins, protected by bivalved indusia consisting of an outer valve of reflexed pinnule tissue and an inner true indusial valve. this marginal soral position is the key reproductive diagnostic of the dicksoniaceae. fronds that unfurl from coiled fiddleheads (croziers). Like all ferns, it reproduces via spores borne on the underside of fertile fronds rather than flowers and seeds, and its life cycle alternates between a dominant sporophyte (the visible plant) and a small, short-lived gametophyte stage.
Reproduction & Propagation
Propagation of Dicksonia berteroana can be achieved through several methods:
- Spores: Collect ripe spores from the underside of fertile fronds, sow on sterilised peat or peat/perlite mix. Do not cover. Keep humid and in bright indirect light. Prothalli (gametophytes) typically develop in 4–12 weeks, and young sporophytes appear after a further 2–6 months.
- Division: Mature clumps with multiple crowns or creeping rhizomes can be divided in spring as new fronds emerge.
- Rhizome cuttings / offsets: Epiphytic genera (Davallia, Polypodium, Phlebodium) can be propagated from 5–10 cm rhizome segments with at least one frond and visible roots.
Cultivation & Substrate
Successful cultivation of Dicksonia berteroana depends on matching three conditions to its natural habitat: consistent moisture without waterlogging, a humus-rich yet well-drained substrate, and the correct light level for its frond type — whether dappled woodland shade, bright filtered light, or, for a handful of rock ferns, direct sun.
Substrate: A moisture-retentive, well-drained, acidic organic substrate replicating the volcanic-derived forest soils of the Juan Fernandez Islands. Suggested composition: 40 percent composted bark fines, 25 percent leaf mould, 20 percent perlite or pumice (ideally volcanic pumice), and 15 percent volcanic gravel or coarse grit. The inclusion of volcanic mineral components reflects the natural substrate and provides beneficial trace elements. Moderately acidic, pH 5.0 to 6.5, reflecting the acidic volcanic soils of the native habitat derived from weathered basalt. Excellent drainage essential despite the species' high moisture needs. The volcanic island substrate is inherently porous and free-draining. Use generous drainage layers at the container base and maintain an open-textured substrate that passes water freely while retaining moisture in the organic fines. Low to moderate. The volcanic soils of the native habitat are not highly fertile, with nutrient cycling primarily through organic decomposition. Light feeding with dilute liquid fertiliser during the growing season is appropriate. Avoid concentrated fertilisers. High. The forest floor in the native habitat is a deep layer of decomposing leaf litter, fern fronds, mosses, and wood debris. Include substantial organic components in the substrate to replicate this environment.
Water: Rainwater (water the trunk!)
Light: Filtered shade to moderate light in the native forest habitat, where the relatively open island forest canopy, composed of endemic trees of moderate stature, allows more light penetration than dense continental rainforest while the persistent cloud cover softens and diffuses the incoming radiation. The species tolerates somewhat brighter conditions than deeply shade-adapted tropical cloud forest species but should be protected from sustained direct midday sun, which would cause frond scorch and desiccation, particularly in combination with wind or low humidity. In cultivation, dappled shade under a deciduous or evergreen canopy, or the filtered light of a well-ventilated conservatory with shade cloth, would be appropriate. Morning sun with afternoon shade is acceptable in cool humid maritime climates.
Humidity: 70-95%
Common Mistakes to Avoid
Treating the species as equivalent to D. antarctica in cold-hardiness is the most common and consequential error; D. berteroana evolved in a frost-free maritime environment and cannot survive the temperatures that D. antarctica tolerates. Allowing humidity to drop below 60 percent for extended periods damages the fronds and stresses the growing point. Neglecting daily trunk-watering in warm weather is the universal Dicksonia cultivation failure. Sourcing material from wild populations without authorisation from CONAF and the Chilean government is illegal and threatens the small remaining natural population. Planting in alkaline or heavy clay soil creates inhospitable root conditions for a species adapted to acidic volcanic soils. Exposing the plant to hot dry continental conditions is unsuitable; the species requires cool maritime humidity.
Seasonal Considerations
The Juan Fernandez Islands have a Mediterranean-influenced oceanic climate with a mild wet winter (May to September) and a warmer somewhat drier summer (October to April), though cloud immersion provides significant moisture year-round at higher elevations where the species grows. In cultivation, maintain consistent moisture and humidity throughout the year, with increased watering during warmer months when evaporation is higher. Protect from frost during winter in any temperate-zone cultivation. No true dormancy occurs, and the species may produce new fronds at any time of year in equable conditions. In the Southern Hemisphere, spring (September to November) is likely the period of maximum new growth, and light feeding during this period supports vigorous frond production.
Diseases & Pests
Common issues affecting Dicksonia berteroana in cultivation:
- Root/rhizome rot: Caused by waterlogged substrate, compacted soil, or overwatering in cool weather. Ensure the growing medium is well-aerated and never let pots sit in standing water for prolonged periods.
- Fungal leaf spot & Botrytis: Brown or grey blotches appear in stagnant, overly humid conditions. Improve air circulation, remove affected fronds, and avoid wetting foliage late in the day.
- Scale insects & mealybugs: The most common fern pests, hiding on stipes and frond undersides. Wipe off with a cotton swab dipped in diluted isopropyl alcohol, or treat with horticultural soap. Many chemical pesticides scorch fern fronds — always test on one frond first.
- Spider mites: Fine webbing and stippled fronds, common in dry indoor air. Raise humidity and rinse fronds regularly with tepid water.
- Frond browning (tip burn): Caused by dry air, direct hot sun, fluoridated or chlorinated tap water (especially in Nephrolepis, Calathea-loving filmy ferns), or soluble-salt build-up from fertiliser. Flush the pot with rainwater and reduce feeding.
Indoor Growing & Terrariums
Dicksonia berteroana can be grown indoors as a houseplant or terrarium subject when its humidity and light requirements are met.
Indoor Setup
- Light: Bright indirect light — an east- or north-facing window, or 30–60 cm under an LED grow light (10–12 hours/day). Most ferns scorch in direct midday sun.
- Humidity: 50–80%. Group plants, stand pots on a pebble-and-water tray, or run a humidifier; misting alone rarely raises ambient humidity enough.
- Temperature: 16–24°C (60–75°F) for most indoor species; avoid cold drafts and hot radiators.
- Substrate: Peat-free potting mix with added perlite and orchid bark for drainage; epiphytic genera (Platycerium, Davallia) grow best mounted on bark or in a bark-heavy orchid mix.
- Water: Keep consistently moist but never waterlogged. Let the top 1–2 cm of substrate dry slightly between waterings in winter.
- Air circulation: A gentle fan discourages fungal leaf spot without drying out the fronds.
Landscape & Garden Use
Dicksonia berteroana can be used in the garden wherever its hardiness and habitat preferences are matched. Ferns are classic choices for shaded borders, woodland gardens, stumperies, rockeries, stream-side plantings, and ground-cover under trees.
Landscape Tips
- Companions: Hostas, Astilbe, Heuchera, Tiarella, Epimedium, hellebores, snowdrops and other shade-tolerant perennials are classic partners.
- Soil preparation: Incorporate leaf mould or composted bark to improve moisture retention and mimic a forest floor.
- Mulching: A 3–5 cm mulch of chipped bark or leaf litter protects the rhizomes, conserves moisture, and slowly releases nutrients.
- Watering: Establish new plantings with regular deep watering during the first growing season; most hardy ferns need only occasional supplemental irrigation once established.
Conservation & Collector Notes
Dicksonia berteroana is an endemic species of the Juan Fernandez Islands, the conservation of which is a high international priority. The islands are a Chilean National Park (1935) and a UNESCO Biosphere Reserve (1977), and significant resources have been invested in invasive species control and native forest restoration by the Chilean government through CONAF, the island municipality, and international partners including the Royal Botanic Garden Edinburgh, Island Conservation, and the Juan Fernandez Islands Conservancy. The species is not subject to CITES trade regulation. Its IUCN status has been assessed as part of the broader evaluation of the Juan Fernandez flora and likely falls within a threatened category given the small total population, highly fragmented habitat, and ongoing threats. The principal threats are invasive species (blackberry, maqui, rats, rabbits, and goats), which continue to degrade native forest despite substantial control efforts, and the inherent vulnerability of a small insular population to stochastic events such as wildfire, severe storms, or disease outbreaks. Climate change may alter rainfall patterns and cloud-base elevation in ways that affect the island's cloud forest ecosystem. Long-term conservation depends on sustained invasive species management, continued forest restoration planting, ex situ conservation through spore banking and international living collections, and the biosecurity measures needed to prevent new invasive introductions.
Collector Notes
Dicksonia berteroana is among the most scientifically interesting and desirable tree fern species for serious collectors and institutional collections, combining extreme rarity, extraordinary oceanic island endemism, a compelling connection to the Robinson Crusoe literary tradition, and the dramatic story of its namesake Carlo Bertero's botanical career and tragic death at sea. Herbarium material is held at the Museo Nacional de Historia Natural in Santiago (SGO), the Royal Botanic Gardens Kew (K), the Royal Botanic Garden Edinburgh (E), and other institutions with significant Pacific and South American collections. Living specimens outside Chile are exceedingly rare and essentially undocumented. Any opportunity to establish ex situ conservation collections through internationally coordinated spore collection programmes would be of enormous scientific and conservation value. The species should be a priority target for collaborative efforts between Chilean conservation authorities and major international botanical gardens.
Ethnobotany & Cultural Significance
The Juan Fernandez Islands were uninhabited before European discovery by the Spanish navigator Juan Fernandez in 1574, so no indigenous ethnobotanical tradition exists. The islands served subsequently as a way station for Spanish colonial shipping, a hideout for pirates and privateers including Alexander Selkirk whose marooning inspired Robinson Crusoe, a penal colony, and a small fishing and lobstering community. Tree ferns were likely used by transient residents for temporary shelter construction and fuel, though no specific records of D. berteroana use exist. The most significant human interaction with the species in the modern era is the conservation programme to save it and its ecosystem from extinction. The archipelago's literary association with Robinson Crusoe gives the islands and their flora a unique cultural resonance that supports conservation advocacy and fundraising, and the tree fern, as one of the most visually striking endemic species, serves as an effective ambassador for the broader conservation effort.
Frequently Asked Questions
Is Dicksonia berteroana from Robinson Crusoe Island?
Yes. The species occurs primarily on Robinson Crusoe Island (formerly Mas a Tierra), where the real-life Alexander Selkirk was marooned from 1704 to 1709, inspiring Daniel Defoe's 1719 novel. The island was officially renamed Isla Robinson Crusoe by the Chilean government in 1966.
Who was Carlo Bertero and what happened to him?
Carlo Giuseppe Bertero (1789 to 1831) was an Italian physician and botanist from Piedmont who collected plants extensively in the Caribbean and South America. He visited Chile and the Juan Fernandez Islands in the late 1820s, making important botanical collections including the type material for many endemic species. He was tragically lost at sea in April 1831 when his vessel disappeared during a voyage from Tahiti.
How did a tree fern reach such remote islands?
By long-distance spore dispersal across the open ocean. Fern spores are microscopic, weighing fractions of a microgram, and can be carried hundreds or thousands of kilometres in atmospheric circulation patterns. The Juan Fernandez Islands are approximately 670 kilometres from continental Chile, a distance well within the documented dispersal range of fern spores.
Can I purchase Dicksonia berteroana from a nursery?
No. The species is not commercially available anywhere in the world. It exists in cultivation only within the Chilean conservation programme on Robinson Crusoe Island and possibly at a very small number of Chilean botanical institutions. Any future availability would need to be through conservation-focused botanical garden collaboration.
What is the main threat to this species?
Invasive plant species, particularly European blackberry and Chilean maqui, that have colonised large areas of the native forest habitat on the Juan Fernandez Islands, forming dense impenetrable thickets that exclude native species. Feral animals (goats, rabbits, rats) compound the problem by damaging native vegetation and preventing natural regeneration. Conservation efforts focus on systematic hand-removal of invasive plants and replanting with nursery-raised native species.
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Quick Reference Summary: Dicksonia berteroana
Golden Rule: Match moisture, light and humidity to each fern’s natural habitat — woodland ferns need shade and humus, rock ferns need drainage, filmy ferns need constant humidity.
Dicksonia berteroana is a tree fern endemic to the Juan Fernandez Islands off the coast of Chile, famously associated with Robinson Crusoe Island. Named after the Italian botanist Carlo Giuseppe Bertero (1789 to 1831), who was tragically lost at sea after collecting on the islands, the species belongs to the family Dicksoniaceae and is distinguished by its soft hairy stipe bases and marginal bivalved sori. It produces a trunk of 2 to 5 metres and a crown of bipinnate fronds in the remnant native cloud forest of these remote volcanic islands. Threatened by invasive species and habitat degradation, it is a high conservation priority within the Juan Fernandez UNESCO Biosphere Reserve. Not commercially available, the species is of exceptional interest to pteridologists and Pacific island flora conservationists as an example of Gondwanan fern lineage persistence on geologically young oceanic islands, and its conservation is inseparable from the broader effort to restore the archipelago's extraordinary endemic vegetation.